In conventional Winchester disk drives, a read/write head or transducer assembly "flies" upon an air cushion or bearing in close proximity, e.g., within seven micro-inches, to a surface of a rotating disk. The disk surface carries a thin film magnetic material having a multiplicity of magnetic storage domains that may be recorded and read back by the head. The read/write transducer assembly, e.g., a well-known combination of transducers, sliders and load beams, is positioned and supported proximate the disk surface using an actuator assembly. The actuator assembly supports the load beams and sliders, and accurately positions the transducers above the disk surface such that data may be read and written from/to the disk. The load beam typically applies a preload force to the slider to urge it toward the disk surface. This force is overcome by the air bearing ensuing during disk rotation.
Actuator assemblies typically contain a driving mechanism to facilitate transducer positioning and a carriage assembly for connecting the driving mechanism to the transducer assembly. Typically, the driving mechanism is either a linear or rotary actuator motor that moves the carriage assembly along a predefined path to accurately position the transducers relative to the disk surface. In high capacity hard disk drives, the actuator motor includes a voice coil operating within a closed loop head position servo.
When disk rotation ceases, the air bearing no longer overcomes the preload force or supports the transducers above the disk surface. In most hard disk drives, when power is removed from the spindle motor that rotates the disk, the transducers come to rest upon the disk surface. To ensure that the transducers do not come to rest upon a portion of the disk that contains recorded data, as the disk drive is powered down, the actuator assembly positions the transducers over a so-called landing or parking zone on the disk surface. Typically, after power has been disconnected from the disk drive, back-EMF energy from the spindle motor is used, in a well-known manner, to power the actuator assembly and position the transducers in the landing zone. Thus, after the disk ceases to rotate, the transducers have been appropriately positioned for parking and come to rest upon the disk surface in the landing zone.
Conventionally, while the disk drive is not operating, friction between the transducers and the disk surface helps to maintain the actuator assembly in a fixed position. However, lateral mechanical shock to the disk drive can cause the transducers to move (slide) radially across the surface of the disk. Such movement, in absence of an air bearing, may result in damage, e.g., abrasions, scratches and dents, to the surface of the disk as well as damage to the sliders and transducers themselves. Such damage can result in a loss of data and/or transducer malfunction that can render the disk drive inoperable.
Consequently, those skilled in the art have employed a wide variety of actuator latching devices to maintain an actuator assembly in a locked position while the disk is not rotating. When the disk has attained a proper rotational velocity to produce a sufficient air bearing to support the transducers, the devices release the actuator assembly and permit it to operate through its limited range of travel relative to the disks.
Generally, there are three well-known approaches: solenoid safety latches, magnetic capture latches, and rigid air vane latches. Each of these latches is discussed below.
Solenoid safety latches typically have a pin, rod or shaft biased into engagement with a movable portion of an actuator assembly by a spring or by magnetic field attraction. The pin, so engaged, immobilizes the actuator assembly. A solenoid, attached to the pin, withdraws the pin from the actuator assembly when the disk attains an appropriate rotational velocity to produce an air bearing. This approach requires a complex electro-mechanical latching apparatus that adds to the size, weight, cost, and power consumption of a disk drive. Examples of solenoid safety latches include U.S. Pat. Nos. 4,881,139; 4,903,157; and, 5,095,395.
Magnetic capture latches typically have a small permanent magnet attached to a movable portion of an actuator assembly and a steel striking plate mounted at a fixed location on the disk drive housing. The permanent magnet and striking plate are positioned such that, when the transducers are positioned in the landing zone, the permanent magnet attaches to the striking plate. The attractive force (latching force) between the permanent magnet and the striking plate immobilizes the actuator assembly. Once the disk has been brought to an appropriate rotational velocity to produce an air bearing, the actuator assembly motor overcomes the latching force and moves the actuator assembly such that the permanent magnet separates from the striking plate. An example of a magnetic capture latch is given in U.S. Pat. No. 5,025,335.
Though typically small in size themselves, such magnetic capture latches require larger actuator motors than disk drives without magnetic catch latches because the actuator assembly motors must be capable of overcoming the latching force as well as positioning the transducers. Further, such disk drives are susceptible to damage from mechanical shocks that have a force greater than the latching force. Such shocks may dislodge the permanent magnet from the striking plate and cause the transducers to move across the surface of the disk in absence of a air bearing; thus, causing damage to the disk drive. Also, the magnetic field may add a deflection bias force to the actuator at the vicinity of innermost data tracks, thereby potentially interfering with, or adding complexity to, the head positioner servo loop. One way of minimizing this bias force is to provide a shifting proximity magnetic capture latch, such as disclosed in U.S. Pat. No. 5,003,422; and, in commonly assigned, copending U.S. patent application Ser. No. 07/964,762 filed on Oct. 22, 1992 now U.S. Pat. No. 5,341,259. Also note commonly assigned U.S. Pat. No. 5,208,713 for its disclosure of a bistable magnetic, electromagnetic actuator latch structure.
Air vane latches typically contain a rigid air vane latch mechanism that engages, through a spring generated bias force, a movable portion of an actuator assembly whenever a disk is not rotating. The air vane latch also contains a rigid, non deformed air vane, extending from or attached to the mechanical latch mechanism. The air vane utilizes the windage from a rotating disk to unlatch the latch mechanism. Specifically, windage from the rotating disk pushes the air vane creating enough force to overcome the bias force and disengage the latch mechanism from the actuator assembly. Examples of air vane latches are described in commonly assigned U.S. Pat. Nos. 4,538,193; 4,647,997; and 4,692,829; and, commonly assigned, copending U.S. patent application Ser. No. 08/005,645, filed on Jan. 19, 1993, now U.S. Pat. No. 5,319,511; and, U.S. Pat. Nos. 5,036,416; and, 5,124,867.
However, to produce a sufficient force to overcome the bias force, such air vane latches require an appropriate air vane surface size and sufficient airflow within the disk enclosure. Such surface size can require excessive spacing between the disk and the drive enclosure. Also, in a multiple-disk drive, the air vane is located between one or more of the disks and, as such, the disks are spaced sufficiently apart to accommodate the air vane structure. Such increased spacing can necessitate increased size, weight and cost of the disk drive.
Therefore, a need exists in the art for a simple, cost efficient latching apparatus that does not require any modification to the size of a disk drive into which it is incorporated.